E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
and Tarpaulings. Soldiers and sailors. Soldiers are now popularly called lobsters, because they are turned red when enlisted into the service. But the term was originally applied to a troop of horse soldiers in the Great Rebellion, clad in armour which covered them as a shell.
Sir William Waller received from London (in 1643) a fresh regiment of 500 horse, under the command of Sir Arthur Haslerig, which were so prodigiously armed that they were called by the kings party the regiment of lobsters. because of their bright iron shells with which they were covered, being perfect cuirassiers, and were the first seen so armed on either side.Clarendon: History of the Rebellion, iii. 91.